My research interests are in the area of solid mechanics and span deformation, fatigue, and fracture. My work is primarily experimental in nature, but also involves theoretical modeling and finite element analysis. The experiments we conduct are typically in support of constitutive modeling, which often requires numerical implementation. The materials we are investigating include metallic alloys (nickel-base superalloys, titanium, aluminum, stainless steel), composites (particle reinforced aluminum, fiber reinforced aluminum, and fiber reinforced titanium), and thin films. The deformation studies include characterizing multiaxial plastic flow in composites by tracking evolution of the yield surface and assessing the direction of the plastic strain increment vector with respect to the yield surface. These results enable us to assess the three primary elements of plasticity models: yield criterion, plastic flow law, and hardening rule. The experiments themselves involve axial-torsion loading of thin walled tubular specimens. Another current deformation project investigates cyclic viscoplastic deformation at elevated temperature where creep, stress relaxation, strain ratcheting, strain rate dependence, load path dependence, and creep-fatigue interaction are activated. Prediction of low cycle fatigue life is dependent on accurate representation of these phenomena.
Technology for structural health monitoring of pump shafts in nuclear power plants is being developed. The technology utilizes torsional vibration monitoring to detect fatigue crack growth. In this work we are seeding cuts and fatigue cracks in testbed shaft systems and developing modeling methods to correlate laboratory test results for closed fatigue cracks and open cuts. In addition, we are developing a life prediction model to estimate remaining useful life based on changes in the vibrational response.
The structural integrity of thin films is important in a number of very different applications. Residual stress in a coating from various deposition processes is being determined from curvature measurements. Failure mechanisms of sculptured thin films are also being investigated to enable us to start to understand the strength and reliability of this new class of coating.